Effect of Shearing Forces and Flocculant Overdose on Filler Flocculation Mechanisms and Floc Properties

Plant-based coagulants/flocculants: characteristics, mechanisms, and possible utilization in treating aquaculture effluent and benefiting from the recovered nutrients

The increasing intensification of the aquaculture industry requires the development of new strategies to reduce the negative impacts of wastewater on the environment. Plant-based coagulants/flocculants, regarded as one of the environmentally friendly technologies for wastewater treatment, show good performance in the removal of suspended solids from wastewater. The aforementioned technology involves the utilization of plants as coagulants/flocculants in the treatment process and produces nontoxic sludge as treatment by-products. The produced sludge could be converted into valuable compounds used in agriculture. This review summarizes coagulation-flocculation by using plant-based coagulants/flocculants, its mechanisms, operational factors that control the treatment process, and its application in the treatment of wastewater, especially aquaculture effluent. Moreover, this work discusses the potential utilization of aquaculture sludge as a valuable compound used in agriculture. The presented review aims to emphasize the potential of using plant-based coagulants/flocculants in the treatment of aquaculture effluent and explore the potential of using the produced sludge as fertilizer for plants to solve problems related to sludge handling and the toxicity of inorganic coagulants in a recirculating aquaculture system. This paper concluded that utilization of recovered nutrients in the form of solids is feasible for agricultural purposes, while a hydroponic system can be used to reclaim the nutrients in the form of solution.

A review of flocculants as an efficient method for increasing the efficiency of municipal sludge dewatering: Mechanisms, performances, influencing factors and perspectives

Mechanical sludge dewatering is one of the stages of the municipal wastewater treatment process, which allows the amount of generated sludge and the cost of its transport and management to be reduced. Achieving a high degree of dewatering is possible thanks to the use of flocculation technology. The article presents issues related to the theory of flocculation, sewage sludge, and its dewatering. The main mechanisms of flocculation, the kinetics of the process, the division of flocculants, and flocculation in dual systems are discussed. The influence of particular parameters on the efficiency of flocculation and the dewatering of sewage sludge was analyed. The assessed parameters are: pH, the presence of salt, the mixing process, the structure and ionicity of chains, and the dose. The results of experimental studies on the dewatering of various types of sludge were compared. The literature review included in the paper helps to better understand the process of flocculation and sludge dewatering, and presents the progress to date and the possible directions for further development in this field.

Research on a new cationic polyacrylamide (CPAM) with a cationic microblock structure and its enhanced effect on sludge condition and dewatering

Flocculation is one of the commonly used sludge conditioning methods in water supply plants, which can improve the sludge dewatering performance by reducing the specific resistance of sludge (SRF), decreasing the amount of sludge, and finally lowering the transportation cost and subsequent disposal cost of sludge. Therefore, it is particularly important to develop new and efficient flocculants. In this paper, the template copolymer of acryloxy trimethylammonium chloride (DAC) and acrylamide (AM) was successfully synthesized by microwave-template copolymerization (MV-TP) using sodium polyacrylate (NaPAA) as template. The template copolymer was analyzed by infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), and scanning electron microscopy (SEM). It was found that this template copolymer had obvious cationic microblock structure. In addition, the test results of association constant (K_M) and polymerization kinetics showed that the MW-TP was assigned to free radical initiated polymerization and the polymerization mechanism was I Zip-up (ZIP). It confirmed the formation of cation fragment structure again. Due to its dense positive charges in this new cationic microblock structure, it greatly improved the functions of electric neutralization, electrical patching, and adsorption bridging. The cationic fragment structure in the template copolymer could help to generate large and dense floc structure and form stable drainage channels. Under external pressure, these large and compact floc structures had greater compressive resistance, which avoided deformation and blockage of drainage channels and voids. It was beneficial to reduce SRF and evidently enhanced sludge dewatering performance.

Ionic strength and polyelectrolyte molecular weight effects on floc formation and growth in Taylor-Couette flows

Polyelectrolyte-driven flocculation of suspended particulate in solution is an important process in a variety of industrial processes such as drinking water treatment and composite material synthesis. Flocculation depends on a wide variety of physicochemical and hydrodynamic properties, which affect floc size, growth rate, and floc morphology. Floc formation and growth behavior is explored here using two different molecular weights of a cationic polyacrylamide flocculant and anisotropic Na-bentonite clay particles under a variety of solution ionic strengths. A Taylor-Couette cell with radial injection capabilities was used to study the effects of solution ionic strength and polyelectrolyte molecular weight on floc size, growth rate, and floc morphology during the flocculation process with a constant global velocity gradient. The floc size generally decreased with increasing ionic strength whereas the floc growth rate initially increased then decreased. This likely occurred due to charge screening effects, where increased bentonite aggregate size and a less expanded polyelectrolyte conformation at higher ionic strengths results in a decreased ability for the polyelectrolyte to bridge multiple bentonite aggregates. The densification of bentonite aggregates at higher ionic strengths resulted in floc morphologies that were more resistant to shear-induced breakage. With the exceptions of optimal dose concentration and dispersion coefficients, there were no clear differences in the floc growth rate behaviors for the two molecular weights studied. This work contributes to an improved understanding of the physicochemical complexities of polyelectrolyte-driven flocculation that can inform dosing requirements for more efficient industrial operations.

Microplastics in Ecosystems: From Current Trends to Bio-Based Removal Strategies

Plastics are widely used due to their excellent properties, inexpensiveness and versatility leading to an exponential consumption growth during the last decades. However, most plastic does not biodegrade in any meaningful sense; it can exist for hundreds of years. Only a small percentage of plastic waste is recycled, the rest being dumped in landfills, incinerated or simply not collected. Waste-water treatment plants can only minimize the problem by trapping plastic particles of larger size and some smaller ones remain within oxidation ponds or sewage sludge, but a large amount of microplastics still contaminate water streams and marine systems. Thus, it is clear that in order to tackle this potential ecological disaster, new strategies are necessary. This review aims at briefly introducing the microplastics threat and critically discusses emerging technologies, which are capable to efficiently clean aqueous media. Special focus is given to novel greener approaches based on lignocellulose flocculants and other biomaterials. In the final part of the present review, it was given a proof of concept, using a bioflocculant to remove micronized plastic from aqueous medium. The obtained results demonstrate the huge potential of these biopolymers to clean waters from the microplastics threat, using flocculants with appropriate structure.

Modification of microcrystalline cellulose with acrylamide under microwave irradiation and its application as flocculant

Grafting polyacrylamide (PAM) chains onto microparticles may combine the advantages of the flocculation property of the former and the fast sedimentation of the later to realize better flocculation performance. In this work, inexpensive microcrystalline cellulose (MCC) microparticles, and monomer of acrylamide (AM) were mixed, and then irradiated under microwave. The obtained material was characterized by Fourier transform infrared spectroscopy and X-ray diffraction, and the results demonstrated successful modification of MCC with AM on the particle surface. The modification procedure has been carefully investigated to obtain an optimum preparation condition. Kaolin suspension was selected as a model to evaluate the flocculation properties of the obtained AM-MCC. Our results indicate that the AM-MCC with the highest grafting ratio of 95.5% exhibits the best flocculation performance, which is even better than that of PAM, and the turbidity can be decreased to 1.4% of the naked kaolin suspension within 2.5 min. Therefore, this work provides a low cost strategy to prepare biodegradable AM-MCC, which may have promising potential application in the water treatment and other fields.

Magnetic flocculants synthesized by Fe3O4 coated with cationic polyacrylamide for high turbid water flocculation

A novel magnetic flocculant (CPAMF) was synthesized by using Fe₃O₄ coated with cationic polyacrylamide (CPAM) for flocculation of high turbid water. The surface morphology and chemical structures of CPAMF were confirmed by Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) was employed to verify the crystal structure of CPAMF. The magnetic property of CPAMF was compared with Fe₃O₄ in this study. The flocculation performance by using flocculants CPAMF was evaluated in high turbid water treatment. The maximum transmittance 92.4% of kaolin suspension was achieved at corresponding optimal flocculation conditions. The result indicated that CPAMF was efficient in high turbid water flocculation. Analysis of FTIR, XRD of flocs, and zeta potential (ZP) of supernatant were accomplished for flocculation mechanism investigation. Because of low recovery factor in reflocculation under the effect of shear force on flocs, the bridging effect was found to be dominant in both acidic and alkaline conditions. Sedimentation experiments under the role of permanent magnet indicated that nano-Fe₃O₄ could effectively improve the settling property of CPAM. Graphical abstract ᅟ.

A review on chitosan-based flocculants and their applications in water treatment

In recent years, the use of chitosan and its derivatives as flocculants in water treatment has received considerable attention due to their many advantages, including their widespread availability, environmental friendliness, biodegradability, and prominent structural features. However, it is a significant strategy for selection and design of the high-performance materials on the basis of their structure-activity relationships. Here we describe several of the chemical modification methods commonly used to prepare chitosan-based flocculants. These methods allow convenient control and adjustment of the structures of the obtained materials to meet the different practical requirements. The influence of structural elements of the chitosan-based flocculants on their flocculation properties are emphasized in this review by examining different flocculation mechanisms and their applications in the treatment of various wastewaters containing different pollutants (insoluble suspended colloids but also dissolved matters). Above all, the chitosan-based flocculants with proper structures by precise structure control bear great application potentials in water treatment.

Evaluation of the Performance of Dual Polyelectrolyte Systems on the Re-Flocculation Ability of Calcium Carbonate Aggregates in Turbulent Environment

Flocculation can be used in turbulent environments resulting in floc breakage due to shearing. The degree of re-flocculation relates directly to product quality and process efficiency. This study aimed at looking for alternatives to improve the re-flocculation ability of aggregates when polyelectrolytes (PEL) are used as flocculation agents. Moreover, because branched PEL have proved previously to lead to high flocculation efficiencies, the work presented focus on the improvement of the re-flocculation ability of branched PEL. Thus, a selection of branched polymers were used primarily as flocculation aid and after flocs break up a linear polymer was added to the system in order to improve re-flocculation. Different mixtures were tested with the objective to try to induce, during re-flocculation, complementary flocculation mechanisms, favoring the patching mechanism. Re-flocculation improved significantly with this strategy. Laser Diffraction Spectroscopy was used to monitor the flocculation and re-flocculation processes supplying information about the floc size and structure. Since inorganic materials, namely bentonite, have been widely used to improve the re-flocculation capacity of polyelectrolytes, the results of using dual polyelectrolyte systems were compared with the effect of adding bentonite to the system.

Effect of charge balance and dosage of polyelectrolyte complexes on the shear resistance of mineral floc strength and reversibility

We evaluated the effect of polyelectrolyte complexes (PEC) with varying balance of charges on the flocculation of precipitated calcium carbonate (PCC) particles. PECs composed of polyacrylamides carrying opposite charges (A-PAM and C-PAM) were investigated in terms of PCC floc shear resistance and re-flocculation effects. Light transmission was used in real time to monitor the dynamics of flocculation under shear fields. Compared to the single polyelectrolytes, PECs greatly enhanced particle re-flocculation while minor differences in shear resistance were observed. Shear resistance and re-flocculation depended strongly on the molecular weight and charge ratio of the PEC components. In order to achieve floc stability and re-flocculation conditions a minimum concentration of charge-asymmetric PEC should be applied.